In ion implantation systems, an ion beam is directed towards a work piece (e.g., a semiconductor wafer, or a display panel), and implants ions into a lattice thereof. Once embedded into the lattice of the workpiece, the implanted ions change the physical and/or chemical properties of the workpiece. Because of this, ion implantation is used in semiconductor device fabrication, in metal finishing, and for various applications in materials science research.
The ion implantation application space is historically divided into low dose (medium current), high energy and high dose (high current) applications.
In high current applications the cross-sectional area of a high current ion beam can vary depending on the extent of self-neutralization occurring in the beam, among other factors. In self-neutralization, which occurs in absence of an electric field, the ion beam can attract free electrons near the beam path. This tends to limit beam “blow-up”, thereby helping to limit the cross-sectional area of the beam to keep the beam “tight”.
In most instances, the cross-sectional area of the beam is less than that of the workpiece and it is helpful to scan the beam over the workpiece to adequately implant the workpiece. Generally, either an electric or magnetic scanner is used in this regard.
One drawback to electric scanners is that, by their very nature they generate an electric field, and thus they attract electrons to positive electrodes or repel them far from negative electrodes. Since the electrodes are typically close to the beam path this tends to remove free electrons from near the beam path. This can cause beam blow up, sometimes resulting in an unmanageably large beam envelope. This large beam envelope can ultimately result in beam current loss.
To limit or avoid beam blow-up and permit partial self-neutralization of the ion beam, magnetic scanners can be used to scan the beam since magnetic scanners do not use biased electrodes. Magnetic scanners generate a time varying magnetic field through which the ion beam passes. The time varying magnetic field diverts or alters the path of the ion beam back and forth in time.
Although a magnetic scanner does not suffer from the space-charge blow-up like an electric scanner, magnetic scanners tend to require high powers to operate. Generally speaking, the higher the operating power, the more expensive the power source and the greater care exercised with respect thereto. Therefore, aspects of the present disclosure relates to techniques for reducing the power needed for magnetic scanners.